Chemical carcinogens modify DNA, resulting in either blocked replication or mutation. The so-called bypass, or translesion synthesis, DNA polymerases were unknown until the late 1990s but are now recognized to play very important roles in the processing of carcinogen-modified DNA. The known eubacterial, archaebacterial, and eukaryotic DNA polymerases are discussed, including what is presently known about their selectivity in copying past DNA adducts, their structures, and their regulation. Overall, DNA polymerases use a variety of means to replicate damaged DNA, although many of the phenomena are now recognized to fall into a limited number of major mechanisms. More insight is still needed to understand the trafficking of DNA (and RNA) polymerases at sites of DNA damage.